In recent years, for example, a liquid crystal display unit has been used widely in liquid crystal televisions, monitors, mobile phones, and the like as a flat panel display having features such as a smaller thickness and a lighter weight than a conventional cathode ray tube. Such a liquid crystal display unit includes an illumination unit (backlight unit) that emits light, and a liquid crystal panel that displays a desired image by serving as a shutter with respect to light from a light source provided in the backlight unit.
The backlight unit as described above is classified roughly into a direct type and an edge-light type depending on the arrangement of the light source with respect to the liquid crystal panel. For example, a liquid crystal display unit for use in mobile equipment such as a mobile phone, a notebook PC, and a PDA generally adopts the edge-light type, which achieves a smaller thickness more easily than the direct type. More specifically, the edge-light type backlight unit includes the light source on a side of the liquid crystal panel for achieving a smaller thickness, and uses a light guide plate that has a light-emitting surface opposed to a non-display surface of the liquid crystal panel so as to irradiate the liquid crystal panel with light from the light source.
Further, a linear light source composed of a cold-cathode tube or a hot-cathode tube has been used as the light source of the backlight unit. However, such a cold-cathode tube or the like contains mercury and has not been easily recyclable when it is discarded, for example. In view of this, it has been proposed to use a light emitting diode (LED) that does not use mercury as the light source in a conventional backlight unit. Meanwhile, there has been a strong demand for the liquid crystal display unit, in particular, the liquid crystal display unit for use in mobile equipment as described above, to be smaller and thinner. As a measure to meet this demand, the light guide plate used in the conventional backlight unit has been made thinner, for example.
However, when the light emitting diode is made smaller, an amount of light emitted therefrom may be reduced significantly. Under the present circumstances, the light emitting diode can be made no smaller than about 300 μm square. Thus, in the conventional backlight unit, when the light guide plate is thinner than the size of the light emitting diode, light from the light emitting diode cannot be incident on the light guide plate sufficiently.
In view of the above, it has been proposed to provide the conventional backlight unit with a light guide block on an incident surface side of the light guide plate as described in JP 2000-249837A, for example. In this conventional backlight unit, it has been considered that light from the light emitting diode can be incident efficiently even on the light guide plate that is thinner than the size of the light emitting diode.